In recent years, the semiconductor light emitting devices using the InAlGaN-type or other nitride semiconductors have been developed. Since the optical transition is of a direct transition-type, a light emitting element having a nitride semiconductor can achieve high efficiency in the light emitting recombination and high luminance. Furthermore, since the transition energy is wide at 2-6.2 eV, it is suitable for a variety of applications. For example, the band gap energy of InyGa1-yN can be changed from 3.4 eV of GaN to 2 eV of InN by the selection of the value of the composition y of indium. Thus, by the combination of the light emitting element with the fluorescent material having the InGaN layer as the light emitting layer, a white light source can be realized. Such a white light source can be used as a back light of a liquid crystal panel or a light source for illumination.
The thin film type LED (Light Emitting Diode) has been known as a type of the semiconductor light emitting devices that use nitride semiconductors. The thin film type LED is prepared by growing a light emitting layer including a nitride semiconductor on a substrate for crystal growth and, after pasting a supporting substrate on top of it, removing the substrate for crystal growth. It is preferable that, on the substrate for crystal growth, from the viewpoint of the crystal growth, a nitride semiconductor having the same properties as the light emitting layer is used. However, as the nitride semiconductor substrate, the material with the presence of the GaN substrate is expensive and it is difficult to apply it for industrial use. The sapphire substrate is stable in the crystal growing atmosphere and, since a small-diameter wafer is available at a relatively low manufacturing cost, it is often used at present. However, since the sapphire substrate has a large non-matching characteristic of the crystal lattice with the nitride semiconductor layer and also has a large difference in the thermal expansion coefficient, many crystal defects are formed on the nitride semiconductor layer grown on the sapphire substrate. Furthermore, since a large-diameter sapphire substrate is expensive, there is also a limit in manufacturing cost reduction of the semiconductor light emitting device.